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A second study done with 73 women receiving adjuvant radiation therapy for breast cancer found similar differences in the patterns and predictors of morning versus evening fatigue.[16] Participants were recruited to the study at the time of their simulation visit and completed baseline questionnaires. Data were then collected on 2 subsequent days, in the morning and at bedtime, each week during radiation therapy; every 2 weeks for 2 months after radiation therapy; and once a month for 2 additional months thereafter. Fatigue was measured with the Lee Fatigue Scale. For the group as a whole, over the 25 weeks of data collection, morning fatigue decreased slightly during radiation therapy and was constant for 4 months afterwards, while evening fatigue increased through radiation therapy and then declined slightly after treatment. Evening fatigue was higher for those who:

Were working.

Had children at home.

Had higher depression scores.

Morning fatigue was higher for those who:

Had more trait anxiety.

Were experiencing sleep disturbance.

Were younger.

Had lower body mass indices.

Advanced disease and comorbidities also added to the severity of morning fatigue.[16][Level of evidence: III]

A number of research studies document the existence of a fatigue syndrome that is not specific to the disease type or radiation site and that demonstrates a gradual decline in fatigue in the patient after treatment is completed.[15,17,18,19,20] Some of these studies suggest, however, that not all patients return to pretreatment energy levels. Specific etiologic factors and correlates of fatigue associated with radiation therapy have not been identified.[12] Risk factors for persistent low energy in cancer patients include older age, advanced disease, and combination-modality therapy.[21]

Fatigue is a dose-limiting toxicity of treatment with a variety of biotherapeutic agents. Biotherapy exposes patients with cancer to exogenous and endogenous cytokines.[22] Biotherapy-related fatigue usually occurs as part of a constellation of symptoms called flulike syndrome. This syndrome includes fatigue, fever, chills, myalgias, headache, and malaise.[23] Mental fatigue and cognitive deficits have also been identified as biotherapy side effects.[24] The type of biotherapeutic agent used may influence the type and pattern of fatigue experienced.